This invention relates to a method for developing a latent relief image in a photoresist material that has been selectively exposed to radiant energy.
Negative and positive photoresist systems are well known in the art. Simply put, a negative photoresist basically consists of polymerizable material which, when exposed to radiant energy, will polymerize to form a hard sheet. It is well known to cover a substrate with a layer of a negative photoresist material which can be polymerized with radiant energy and then expose selected areas, such as by exposing image-wise through a mask, of the covering material to radiant energy to thereby form a surface that has areas of polymerized and unpolymerized material. This technique creates what is known in the art as a latent image. A relief image is then formed by eluting the layer with a solvent that preferentially dissolves the unpolymerized areas of the layer. Typically, this is achieved by spray washing the layer with a solvent for the unpolymerized material.
In a positive photoresist system, those areas that have been exposed to radiant energy will become more soluble in a selected solvent after exposure. The exposed areas are then preferentially dissolved with a liquid solvent, again such as by being spray washed.
In essence, therefore, in a negative photoresist system the unexposed areas are dissolved, and in a positive photoresist system the exposed areas are dissolved, by selected liquid solvent systems.
Such methods of forming a latent image and subsequently removing selected material by solvent spray washing is in wide commercial use. There are, however, some disadvantages associated with the solvent spray wash removal technique and, indeed, any solvent liquid wash removal technique. Such techniques are typically cumbersome processes that do not always lend themselves to a large scale production facility. Furthermore, large amounts of solvent material are used in such processes. These solvents, especially those that are used with negative photoresist systems, are generally organic materials which are typically very expensive and, furthermore, disposal of spent solvents is often very difficult and costly.
In negative photoresists, such problems are magnified when the layer containing the polymerizable material is stored for any length of time, especially when the material is of the kind that contains a carrier solvent. Such polymerized material, when first laid down on a film, is tacky. Such tackiness can be attributed to the material's carrier solvent. Over time, the solvent will evaporate and the polymerizable material will harden and will subsequently be more difficult to remove by liquid solvent wash. This aging effect may be less pronounced in positive photoresist systems.
It would be advantageous, therefore, to have a method of substantially reducing the amount of time devoted to the solvent spray washing step without deteriorating the developed latent image.